Heat transfer unit for process fluids

ABSTRACT

A heat transfer unit includes an inlet manifold; an outlet manifold spaced from the inlet manifold; and a plurality of conduits coupling the inlet manifold to the outlet manifold, wherein at least on the conduits is coupled to the outlet manifold at an oblique angle. In one form, the conduit includes a L-Coil. In another form, the conduit includes a D-Coil. In another form, the conduit includes a coil having two or more C-shaped sections. Each conduit includes a section arranged in an interior space of a heater box, and at least one heater is arranged in the interior space of the heater box.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosure relates to a low pressure drop heat transfer unit forprocess fluids.

2. Description of the Related Art

Various catalytic conversion processes are known in the petrochemicalindustry. For example, the catalytic reforming of a hydrocarbonfeedstream (e.g., a naphtha feedstream) to produce aromatics (e.g.,benzene, toluene, and xylenes) is described in U.S. Patent ApplicationPublication Nos. 2012/0277501, 2012/0277502, 2012/0277503, 2012/0277504,and 2012/0277505. The catalytic dehydrogenation of a paraffin stream toyield olefins is described in U.S. Pat. No. 8,282,887.

Catalytic reforming and catalytic dehydrogenation processes areendothermic and therefore, heat must be added to maintain thetemperature of the reactions. U.S. Patent Application Publication No.2012/0275974 describes the use of interbed heaters to maintain thetemperature of reaction in the catalytic reactor of a reforming process.Example heaters for process fluids can also be found in U.S. Pat. Nos.8,176,974 and 7,954,544.

Aromatics yield from a catalytic reforming unit and olefin yield from acatalytic dehydrogenation unit increase, while yield of undesirableproducts from competing cracking reactions decreases, with lesseningoperating pressure. Thus, it may be advantageous to minimize reactionzone operating pressure.

The hot residence time of a process stream before the product streamleaves a reactor (also known as hot volume) can also be critical to thecatalytic selectivity to desired products for thermally sensitiveprocesses such as catalytic reforming and catalytic dehydrogenation. Hotresidence time reduction can be critical in reactor circuit non-catalystvolumes in order to prevent yield loss (aromatics or olefins) fromcompeting thermal cracking reactions.

Thus, the design of heaters used in catalytic reforming and catalyticdehydrogenation processes to heat the feed upstream of each reactor canbe guided by two criteria, pressure drop and hot residence time. Whilethe overall low operating pressure benefits the yields from theprocesses, it is more beneficial to use the available pressure dropdiligently in a reactor circuit. The use of the available pressure dropfurther upstream in the reactor circuit is least detrimental. The use ofhigher pressure drop further upstream in the reactor circuit reducesyields to a lesser extent. However, it reduces the hot residence time(thus thermal cracking) in the upstream heaters where the processstreams are often more susceptible to thermal cracking than in thedownstream heaters.

Thermal expansion and contraction in heater coils is yet another designconsideration. Specifically, the heater coils must be able to withstandhigh process temperatures and metallurgical changes and mechanicalstress.

Therefore, what is needed is an improved heat transfer unit for processfluids wherein the heat transfer unit provides low pressure drop butalso the flexibility to withstand thermal expansion/contraction in theheater coils.

SUMMARY OF THE INVENTION

The foregoing needs are met by a heat transfer unit for process fluids.The heat transfer unit includes an inlet manifold; an outlet manifoldspaced from the inlet manifold; and a plurality of conduits coupling theinlet manifold to the outlet manifold, wherein at least one of theconduits is coupled to the outlet manifold at an oblique angle.

In one version of the heat transfer unit, at least one of the conduitsincludes a L-Coil.

In another version of the heat transfer unit, at least one of theconduits includes a D-Coil.

In another version of the heat transfer unit, at least one of theconduits includes a coil having a plurality of generally C-shapedsections.

In another version of the heat transfer unit, at least one of theconduits is coupled to the outlet manifold at an angle between aboutfive and eighty-five degrees.

In another version of the heat transfer unit, at least one of theconduits is coupled to the outlet manifold at an angle between aboutthirty and sixty degrees.

In another version of the heat transfer unit, each of the conduits iscoupled to the outlet manifold at an oblique angle.

In another version of the heat transfer unit, each conduit includes asection arranged in an interior space of a heater box and wherein atleast one heater is arranged in the interior space of the heater box.

In another aspect, the invention provides an L-Coil heat transfer unitfor process fluids. The L-Coil heat transfer unit includes an inletmanifold; an outlet manifold spaced from the inlet manifold; and anL-Coil coupled between the inlet manifold and the outlet manifold. TheL-Coil includes a horizontal leg and a vertical leg, wherein thehorizontal leg is coupled to the outlet manifold at an oblique anglesuch that a flow aperture formed therebetween defines an oblong profile.

In one version of the L-Coil heat transfer unit, a plurality of L-Coilsare coupled to the outlet manifold at an oblique angle.

In another version of the L-Coil heat transfer unit, the L-Coil isarranged at between about a thirty and sixty degree angle relative tothe outlet manifold.

In another version of the L-Coil heat transfer unit, the L-Coil isarranged at between about a five and eighty-five degree angle relativeto the outlet manifold.

The L-Coil heat transfer unit can further comprise a heater arrangedsubstantially adjacent a bottom of the L-Coil heat transfer unit.

The L-Coil heat transfer unit can include a section arranged in aninterior space of a heater box.

In another aspect, the invention provides a D-Coil heat transfer unitfor process fluids. The D-Coil heat transfer unit includes an inletmanifold; an outlet manifold spaced from the inlet manifold; and aD-Coil coupled between the inlet manifold and the outlet manifold, TheD-Coil includes an inlet section and an outlet section, and the inletsection is coupled to the inlet manifold at an oblique angle, and theoutlet section is coupled to the outlet manifold at an oblique angle.

In one version of the D-Coil heat transfer unit, a flow aperture formedbetween the outlet section and the outlet manifold defines an oblongprofile.

In another version of the D-Coil heat transfer unit, a plurality ofD-Coils are coupled to the inlet manifold at an oblique angle and arecoupled to the outlet manifold at an oblique angle.

In another version of the D-Coil heat transfer unit, the inlet sectionis arranged at between about a thirty and sixty degree angle relative tothe inlet manifold, and the outlet section is arranged at between abouta thirty and sixty degree angle relative to the outlet manifold.

In another version of the D-Coil heat transfer unit, the D-Coil includesa section arranged in an interior space of a heater box. At least oneheater can be arranged in the interior space of the heater box.

In a low pressure drop heater design, the heater manifold may accountfor close to 50% of the total pressure heater pressure drop. Themanifold pressure drop is mainly due to the entrance and exit frictionallosses from heater tubes to the heater outlet and inlet.

The invention provides a heat transfer unit with an L-coil design thatdecreases pressure drop. In one non-limiting example of the heattransfer unit, an angled entrance to the heater outlet manifold is usedwith the L-coil design. An angled entrance results in an ellipticalopening into the manifold. This lowers the inlet velocity and thevelocity is in the same direction as the process fluid flow resulting inan additional decrease in a pressure drop. An angled inlet into theheater outlet manifold also provides a longer horizontal arm in anL-heater coil. This in turn gives more flexibility to the heater coilfor vertical compression and tension. A longer horizontal arm of theL-Coil can provide better flexibility in vertical movements.

The invention also provides a heat transfer unit with a D-Coil tointegrate the benefits for low pressure drop design with an improvedflexibility. A D-coil achieves an added reduction in pressure drop byhaving an angled entry into and exit from, inlet and outlet manifolds,respectively. In addition, a D-Coil provides a better flexibility forvertical movements in a heater coil.

The invention demonstrates that an angled connection from heaterconduits to the manifold is preferably used and more preferably, anangled connection is used at an outlet manifold connection. Thisprovides pressure drop reduction due to a bigger opening at theconnection (thus lower frictional loss) and less turbulence (via sameflow direction) with more flexibility for vertical movements. Thepressure drop reduction by angled connection may be more at the outletmanifold connection than the inlet connection due to higher designedvelocity at the outlet. The pressure reduction benefit can be moreprominent in the low pressure drop heater design. The design can also beused for higher pressure drop heater designs. However, yield benefitsfrom reduced heater drop may be less.

It is therefore an advantage of the invention to provide a low pressuredrop heat transfer unit for process fluids.

It is another advantage of the invention to provide a heat transfer unitfor process fluids in a process where pressure drop affects productyields.

These and other features, aspects, and advantages of the presentinvention will become better understood upon consideration of thefollowing detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view of a prior art U-Coil heat transfer unit.

FIG. 2 is a perspective view of the U-Coil heat transfer unit of FIG. 1.

FIG. 3 is a perspective view of a prior art L-Coil heat transfer unit.

FIG. 4 is a side view of the L-Coil heat transfer unit of FIG. 3.

FIG. 5 is an end view of the L-Coil heat transfer unit of FIG. 3.

FIG. 6 is a top view of the L-Coil heat transfer unit of FIG. 3.

FIG. 7 is a side view of an outlet manifold of the L-Coil heat transferunit of FIG. 3.

FIG. 8 is a perspective view of an L-Coil heat transfer unit accordingto one embodiment of the invention.

FIG. 9 is a side view of the L-Coil heat transfer unit of FIG. 8.

FIG. 10 is an end view of the L-Coil heat transfer unit of FIG. 8.

FIG. 11 is a top view of the L-Coil heat transfer unit of FIG. 8.

FIG. 12 is a side view of an outlet manifold of the L-Coil heat transferunit of FIG. 8.

FIG. 13 is a perspective view of an L-Coil heat transfer unit accordingto one embodiment of the invention.

FIG. 14 is a side view of the L-Coil heat transfer unit of FIG. 13.

FIG. 15 is an end view of the L-Coil heat transfer unit of FIG. 13.

FIG. 16 is a top view of the L-Coil heat transfer unit of FIG. 13.

FIG. 17 is a perspective view of an L-Coil heat transfer unit accordingto one embodiment of the invention.

FIG. 18 is a side view of the L-Coil heat transfer unit of FIG. 17.

FIG. 19 is an end view of the L-Coil heat transfer unit of FIG. 17.

FIG. 20 is a top view of the L-Coil heat transfer unit of FIG. 17.

FIG. 21 is a perspective view of a D-Coil heat transfer unit accordingto one embodiment of the invention.

FIG. 22 is a side view of the D-Coil heat transfer unit of FIG. 21.

FIG. 23 is an end view of the D-Coil heat transfer unit of FIG. 21.

FIG. 24 is a top view of the L-Coil heat transfer unit of FIG. 21.

FIG. 25 is a perspective view of a D-Coil heat transfer unit accordingto one embodiment of the invention.

FIG. 26 is a side view of the D-Coil heat transfer unit of FIG. 25.

FIG. 27 is an end view of the D-Coil heat transfer unit of FIG. 25.

FIG. 28 is a top view of the L-Coil heat transfer unit of FIG. 25.

FIG. 29 is a side view of a Triple C-Coil heat transfer unit accordingto one embodiment of the invention.

Like reference numerals will be used to refer to like parts from Figureto Figure in the following description of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Catalytic reactor systems may use U-Coil heaters for heating fresh feedand reheating feed between reactors. A U-Coil style heater may bedesirable due to low process side pressure drop. An example U-Coil styleheat transfer unit 10 is shown in FIGS. 1 and 2 and includes an inletmanifold 14, an outlet manifold 18, a heater box 19, and a plurality ofU-coils 22 arranged for fluid communication therebetween. A number ofburners or heaters 26 are arranged adjacent the axial ends of themanifolds 14, 18. The coils in this embodiment and the other embodimentsdescribed herein may be formed from a stainless steel (e.g., anaustenitic 300 series stainless steel such as 347) or a steel such as9-Chrome-Moly Steel.

Alternatively, catalytic reactor systems may use L-Coil heaters forheating fresh feed and reheating feed between reactors. An exampleL-Coil style heat transfer unit 30 is shown in FIGS. 3-7 and includes aninlet manifold 34, an outlet manifold 38, a heater box 39, and aplurality of L-coils 42 arranged for fluid communication therebetween.FIG. 7 shows apertures 46 arranged in the outlet manifold 38 where theoutlet manifold 38 couples with the L-Coils 42. As clearly shown in FIG.7, in this arrangement the apertures 46 are substantially circular.

FIGS. 8-12 show an L-Coil heat transfer unit 50 according to one aspectof the invention. The L-Coil heat transfer unit 50 includes an inletmanifold 54 arranged to receive a process fluid, an outlet manifold 58arranged to provide the process fluid to a downstream location, a heaterbox 59, and a plurality of L-Coils 62 arranged therebetween.

The L-Coils 62 are preferably welded to the inlet manifold 54 and theoutlet manifold 58 to provide a hermetic seal. As is clearly visible inFIG. 11, the L-Coils 62 are arranged at an oblique angle relative to alongitudinal axis A of the outlet manifold 58. As shown in FIGS. 3-7,the current state-of-the-art is to have L-Coils arranged perpendicularto an outlet manifold (i.e., arranged at a ninety-degree angle (90°)).In a preferred embodiment, the L-Coils 62 are rotated relative to thelongitudinal axis A by about forty-five degrees (45°). In otherembodiments, the L-Coils 62 are rotated relative to the longitudinalaxis A by between about thirty and sixty degrees (30-60°). In stillother embodiments, the L-Coils 62 are rotated relative to thelongitudinal axis A by between about twenty and 70 degrees (20-70°). Instill other embodiments, the L-Coils 62 are rotated relative to thelongitudinal axis A by between about five and eighty-five degrees(5-85°).

As shown in FIG. 10, the inlet manifold 54 is horizontally spaced fromthe outlet manifold 58 by a horizontal distance. Additionally, eachL-Coil 62 includes a horizontal leg 66 and a vertical leg 70.Non-limiting example length ranges for the horizontal leg 66 are 0.30 to7.62 meters (1-25 feet), or 0.61 to 6.10 meters (2-20 feet), or 1.52 to4.57 meters (5-15 feet). Non-limiting example length ranges for thevertical leg 70 are 6.10 to 24.38 meters (20-80 feet), or 9.14 to 21.34meters (30-70 feet), or 12.19 to 18.29 meters (40-60 feet), or 13.72 to16.76 meters (45-55 feet). The oblique arrangement of the L-Coils 62provides a longer horizontal leg 66 relative to the horizontal distancebetween the inlet manifold 54 and the outlet manifold 58 as comparedwith a perpendicular arrangement. This longer horizontal leg 66 allowsfor more flexibility in the system for better response to thermal andmechanical stresses.

Turning to FIG. 12, the outlet manifold 58 is shown removed from theL-Coil heat transfer unit 50. L-Coil outlet apertures 74 are clearlyvisible and provide an oval or oblong or elliptical communicationpathway between the L-Coils 62 and the outlet manifold 58. The L-Coiloutlet apertures 74 have a larger sectional area as compared to theapertures 46 shown in FIG. 7.

In one embodiment, the length of the inlet manifold 54 and outletmanifold 58 in the longitudinal direction is about fifteen meters (about50 feet) or more. In other embodiments, the installation may be smalleror larger, as desired. The L-Coils 62 may be spaced apart by about fiftycentimeters (about 10 feet). In other embodiments, more or less spacingmay be desirable. The L-Coil heat transfer unit 50 may include up toabout eighteen-hundred (1800) L-Coils 62. In other embodiments, theL-Coil heat transfer unit 50 may include more or less L-Coils 62, asdesired.

An additional feature of the L-Coil heat transfer unit 50 is the abilityto position a burner 78 in a variety of locations and arrangements. Asshown in FIG. 10, the burner 78 may be arranged near the inlet manifold54 at the bottom of the heater box 59 and arranged under the L-Coils 62.The burner 78 may extend the full longitudinal length of the L-Coil heattransfer unit 50. In other arrangements, two or more burners 78 may beused (see FIG. 15) and may be arranged elevated above the inlet manifold54, arranged only at one or two ends of the L-Coil heat transfer unit50, or arranged differently, as desired. The L-Coil heat transfer unit50 provides a significant advantage in the flexibility of how theL-Coils 62 are heated as compared to prior art U-Coil designs whereinhot spots are a significant concern and inhibit the use of burnersarranged near the floor or inlet manifold 54. This flexibility will bereadily appreciated by those skilled in the art.

The L-Coil heat transfer unit 50 provides an advantageous fluid flowpattern (shown in dash lines in FIG. 8) that reduces the fluid frictionand therefore reduces the pressure drop through the L-Coil heat transferunit 50 compared to other heat transfer solutions. In other embodiments,other flow patterns are feasible. For example, the inlet manifold 54flow may originate on the left (as shown in FIG. 8), or the outletmanifold 58 and the inlet manifold 54 may be switched such that fluidflow is substantially reversed from what is shown.

Turning now to FIGS. 13-16, another L-Coil heat transfer unit 50′ isshown. The L-Coil heat transfer unit 50′ is substantially similar to theL-Coil heat transfer unit 50 but includes a larger horizontal spacingbetween an inlet manifold 54′ and an outlet manifold 58′ and acorrespondingly longer horizontal leg 66′ on each L-Coil 62′. Allcomponents of the L-Coil heat transfer unit 50′ have been numberedsimilar to the L-Coil heat transfer unit 50 with prime numbers. Anincreased horizontal leg 66′ length provides an L-Coil 62′ with moreflexibility with respect to thermal and mechanical stresses.

Turning now to FIGS. 17-20, another L-Coil heat transfer unit 50″ isshown. The L-Coil heat transfer unit 50″ is substantially similar to theL-Coil heat transfer unit 50 but includes a larger horizontal spacingbetween an inlet manifold 54″ and an outlet manifold 58′″, and acorrespondingly longer horizontal leg 66″ on each L-Coil 62″. Allcomponents of the L-Coil heat transfer unit 50″ have been numberedsimilar to the L-Coil heat transfer unit 50 with prime numbers. Anincreased horizontal leg 66″ length provides an L-Coil 62″ with moreflexibility with respect to thermal and mechanical stresses.

Turning to FIGS. 21-24, a D-Coil heat transfer unit 100 includes aninlet manifold 104, and outlet manifold 108, a heater box 109, and aplurality of D-Coils 112 arranged therebetween. The distance between theinlet manifold 104 and the outlet manifold 108 may be in the range of6.10 to 24.38 meters (20-80 feet), or 9.14 to 21.34 meters (30-70 feet),or 12.19 to 18.29 meters (40-60 feet), or 13.72 to 16.76 meters (45-55feet). Each D-Coil 112 includes an oblique inlet section 116, an outletsection 122, and a transfer section 124 therebetween. Non-limitingexample length ranges for the inlet section 116 and the outlet section122 are 0.30 to 7.62 meters (1-25 feet), or 0.61 to 6.10 meters (2-20feet), or 1.52 to 4.57 meters (5-15 feet). Non-limiting example lengthranges for the transfer section 124 are 9.14 to 13.72 meters (30-45feet), or 12.19 to 14.68 meters (40-48 feet).

The illustrated inlet section 116 is arranged at an oblique anglerelative to a longitudinal axis of the inlet manifold 104. In theillustrated embodiment, the inlet section 116 is arranged at about aforty-five degree angle (45°) relative to the longitudinal axis of theinlet manifold 104. In other embodiments, the inlet section 116 isarranged at between about thirty and sixty degrees (30-60°) relative tothe longitudinal axis of the inlet manifold 104. In still otherembodiments, the inlet section 116 is arranged at between about twentyand seventy degrees (20-70°) relative to the longitudinal axis of theinlet manifold 104. In still other embodiments, the inlet section 116 isarranged at between about five and eighty-five degrees (5-85°) relativeto the longitudinal axis of the inlet manifold 104.

The outlet section 122 is arranged at an oblique angle relative to alongitudinal axis of the outlet manifold 108. In the illustratedembodiment, the outlet section 122 is arranged at about a forty-fivedegree angle (45°) relative to the longitudinal axis of the outletmanifold 108. In other embodiments, the outlet section 122 is arrangedat between about thirty and sixty degrees (30-60°) relative to thelongitudinal axis of the outlet manifold 108. In other embodiments, theoutlet section 122 is arranged at between about twenty and seventydegrees (20-70°) relative to the longitudinal axis of the outletmanifold 108. In still other embodiments, the outlet section 122 isarranged at between about five and eighty-five degrees (5-85°) relativeto the longitudinal axis of the outlet manifold 108.

As a result of the oblique relation between the D-Coils 112 and theinlet and outlet manifolds 104, 108, the flow apertures formed at thejunction between the D-Coils 112 and the inlet and outlet manifolds 104,108 are oval or oblong or elliptical as described above with respect toapertures 74.

The D-Coil heat transfer unit 100 provides an advantageous fluid flowpattern (shown in dash lines in FIG. 22) that reduces the fluid frictionand therefore reduces the pressure drop through the D-Coil heat transferunit 100 compared to other heat transfer solutions. In otherembodiments, other flow patterns are feasible.

FIGS. 25-28 show a D-Coil heat transfer unit 100′ similar to the D-Coilheat transfer unit 100 and is labeled with prime numbers. The inletsections 116′ and the outlet sections 122′ are of decreased lengthcompared to the inlet sections 116 and the outlet sections 122 in theembodiment of FIGS. 21-24.

Turning to FIG. 29, a Triple C-Coil heat transfer unit 200 includes aninlet manifold 204, an outlet manifold 208, a heater box, and aplurality of Triple C-Coils 210 arranged therebetween. The distancebetween the inlet manifold 204 and the outlet manifold 208 may be in therange of 6.10 to 24.38 meters (20-80 feet), or 9.14 to 21.34 meters(30-70 feet), or 12.19 to 18.29 meters (40-60 feet), or 13.72 to 16.76meters (45-55 feet). Each Triple C-Coil 210 includes a generallyC-shaped inlet section 216, a generally C-shaped outlet section 222, anda generally C-shaped transfer section 212 therebetween.

The illustrated inlet section 216 is arranged at an oblique anglerelative to a longitudinal axis of the inlet manifold 204. In theillustrated embodiment, the junction of the inlet section 216 isarranged at about a forty-five degree angle (45°) relative to thelongitudinal axis of the inlet manifold 204. See angle C in FIG. 29. Inother embodiments, the junction of the inlet section 216 is arranged atbetween about thirty and sixty degrees (30-60°) relative to thelongitudinal axis of the inlet manifold 204. In still other embodiments,the junction of the inlet section 216 is arranged at between abouttwenty and seventy degrees (20-70°) relative to the longitudinal axis ofthe inlet manifold 204. In still other embodiments, the junction of theinlet section 216 is arranged at between about five and eighty-fivedegrees (5-85°) relative to the longitudinal axis of the inlet manifold204.

The outlet section 222 is arranged at an oblique angle relative to alongitudinal axis of the outlet manifold 208. In the illustratedembodiment, the junction of the outlet section 222 is arranged at abouta forty-five degree angle (45°) relative to the longitudinal axis of theoutlet manifold 208. See angle D in FIG. 29. In other embodiments, thejunction of the outlet section 222 is arranged at between about thirtyand sixty degrees (30-60°) relative to the longitudinal axis of theoutlet manifold 208. In other embodiments, the junction of the outletsection 222 is arranged at between about twenty and seventy degrees(20-70°) relative to the longitudinal axis of the outlet manifold 208.In still other embodiments, the junction of the outlet section 222 isarranged at between about five and eighty-five degrees (5-85°) relativeto the longitudinal axis of the outlet manifold 208.

As a result of the oblique relation between the Triple C-Coils 210 andthe inlet and outlet manifolds 204, 208, the flow apertures formed atthe junction between the Triple C-Coils 210 and the inlet and outletmanifolds 204, 208 are oval or oblong or elliptical as described abovewith respect to apertures 74.

The Triple C-Coil heat transfer unit 200 provides an advantageous fluidflow pattern that reduces the fluid friction and therefore reduces thepressure drop through the Triple C-Coil heat transfer unit 200 comparedto other heat transfer solutions. In other embodiments, other flowpatterns are feasible.

In one aspect, the invention provides a catalytic dehydrogenationprocess that includes passing a hydrocarbon feed stream through any ofheat transfer units 10, 30, 50, 50′, 50″, 100, 100′, 200, and thenpassing the heated hydrocarbon feed stream and a catalyst into a reactorthereby creating a product stream.

In another aspect, the invention provides, a catalytic reforming processthat includes passing a hydrocarbon feed stream through any of heattransfer units 10, 30, 50, 50′, 50″, 100, 100′, 200, and then passingthe heated hydrocarbon feed stream and a catalyst into a reactor therebycreating a product stream.

Thus, the invention provides a heat transfer unit for process fluids.While use of the heat transfer unit is not limited to any process, theheat transfer unit can be particularly beneficial in heating processfluids in: (i) the catalytic reforming of a hydrocarbon feedstream(e.g., a naphtha feedstream) to produce aromatics (e.g., benzene,toluene and xylenes) (see, e.g., U.S. Patent Application PublicationNos. 2012/0277501, 2012/0277502, 2012/0277503, 2012/0277504, and2012/0277505); and (ii) the catalytic dehydrogenation of a paraffinstream to yield olefins (see, e.g., U.S. Pat. No. 8,282,887).

Although the invention has been described in considerable detail withreference to certain embodiments, one skilled in the art will appreciatethat the present invention can be practiced by other than the describedembodiments, which have been presented for purposes of illustration andnot of limitation. Therefore, the scope of the appended claims shouldnot be limited to the description of the embodiments contained herein.

1. A heat transfer unit for process fluids, the heat transfer unitcomprising: an inlet manifold; an outlet manifold spaced from the inletmanifold; and a plurality of conduits coupling the inlet manifold to theoutlet manifold, wherein at least one of the conduits is coupled to theoutlet manifold at an oblique angle.
 2. The heat transfer unit of claim1, wherein at least one of the conduits includes a L-Coil.
 3. The heattransfer unit of claim 1, wherein at least one of the conduits includesa D-Coil.
 4. The heat transfer unit of claim 1, wherein at least one ofthe conduits includes a coil having a plurality of generally C-shapedsections.
 5. The heat transfer unit of claim 1, wherein at least one ofthe conduits is coupled to the outlet manifold at an angle between aboutfive and eighty-five degrees.
 6. The heat transfer unit of claim 1,wherein at least one of the conduits is coupled to the outlet manifoldat an angle between about thirty and sixty degrees.
 7. The heat transferunit of claim 1, wherein each of the conduits is coupled to the outletmanifold at an oblique angle.
 8. The heat transfer unit of claim 1,wherein each conduit includes a section arranged in an interior space ofa heater box and wherein at least one heater is arranged in the interiorspace of the heater box.
 9. An L-Coil heat transfer unit for processfluids, the L-Coil heat transfer unit comprising: an inlet manifold; anoutlet manifold spaced from the inlet manifold; and an L-Coil coupledbetween the inlet manifold and the outlet manifold, the L-Coil includinga horizontal leg and a vertical leg, the horizontal leg coupled to theoutlet manifold at an oblique angle such that a flow aperture formedtherebetween defines an oblong profile.
 10. The L-Coil heat transferunit of claim 9, wherein a plurality of L-Coils are coupled to theoutlet manifold at an oblique angle.
 11. The L-Coil heat transfer unitof claim 9, wherein the L-Coil is arranged at between about a thirty andsixty degree angle relative to the outlet manifold.
 12. The L-Coil heattransfer unit of claim 9, wherein the L-Coil is arranged at betweenabout a five and eighty-five degree angle relative to the outletmanifold.
 13. The L-Coil heat transfer unit of claim 9, furthercomprising a heater arranged substantially adjacent a bottom of theL-Coil heat transfer unit.
 14. The L-Coil heat transfer unit of claim 9,wherein the L-Coil includes a section arranged in an interior space of aheater box.
 15. A D-Coil heat transfer unit for process fluids, theD-Coil heat transfer unit comprising: an inlet manifold; an outletmanifold spaced from the inlet manifold; and a D-Coil coupled betweenthe inlet manifold and the outlet manifold, the D-Coil including aninlet section and an outlet section, the inlet section coupled to theinlet manifold at an oblique angle, the outlet section coupled to theoutlet manifold at an oblique angle.
 16. The D-Coil heat transfer unitof claim 15, wherein a flow aperture formed between the outlet sectionand the outlet manifold defines an oblong profile.
 17. The D-Coil heattransfer unit of claim 15, wherein a plurality of D-Coils are coupled tothe inlet manifold at an oblique angle and are coupled to the outletmanifold at an oblique angle.
 18. The D-Coil heat transfer unit of claim15, wherein the inlet section is arranged at between about a thirty andsixty degree angle relative to the inlet manifold, and wherein theoutlet section is arranged at between about a thirty and sixty degreeangle relative to the outlet manifold.
 19. The D-Coil heat transfer unitof claim 15, wherein the D-Coil includes a section arranged in aninterior space of a heater box.
 20. The D-Coil heat transfer unit ofclaim 19, wherein at least one heater is arranged in the interior spaceof the heater box.